Climate Trends

Since the last ice age approximately 10,000 years BP, the land has risen, lake drainages have changed and the climate has gone through periods of warming and cooling. In the past hundred years, as a result of human activities, greenhouse gases in the atmosphere have increased to levels that scientists have concluded are changing our climate. (NRCan, 2006)

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Climate Variable
Impact and System Response

Trends and Forecasts

International:

Following much research and analysis, the Intergovernmental Panel on Climate Change (IPCC), the leading international body charged with deciphering what climate change holds for our future, concludes that the "warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level" (IPCC, 2007).

The IPCC expects that warming in the 21st century will be greatest over land, and at most in the higher northern latitudes. It further suggests that it is very likely that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent.

In both hemispheres mountain glaciers and snow cover have declined, contributing to sea level rise. In the Arctic, in particular, over the last 100 years, temperatures have been increasing at almost twice the global average rate.

National:

For most of Canada, this translates into temperature increases both on a seasonal basis, with winters warming more than summers, and on a daily basis, with evenings warming more than days. Along with increased warming, Canada is expected to experience changes in precipitation patterns, changes in climate variability, and shifts in the frequency and intensity of extreme climate events (NRCan, 2004).

These projected changes to Canada's climate will have far reaching impacts, influencing everything from forest composition, to aquatic and terrestrial life, to agriculture. As with all environmental change, the net impact of warmer temperatures is uncertain. Forests for example, could benefit from a longer growing season. These benefits, however, would likely be offset by associated increases in moisture stress, ecosystem instability, and increases in the frequency and intensity of forest fires, insect outbreaks and extreme weather events.

Regional:

Closer to home, some researchers predict that the Great Lakes and southern Ontario can expect annual temperature increases of about 2 to 6 degrees Celsius, increases in the number of hot days (higher than 30 degrees Celsius), and more frequent, more intense, and longer heat waves.

Projections of warmer temperatures are consistent with observed trends in the region, where the frost-free period has lengthened and total annual snowfall has decreased. Snow cover, depth and duration have also been reduced, and lake ice coverage has declined, with later dates of freezing, and earlier ice-off dates

As temperatures rise in southern Ontario, annual precipitation is expected to become more variable, with a decline of up to 10% for most of southern Ontario (MNR, 2007). An increase in occurrence and intensity of extreme rainfall events is also expected. The warmer temperatures are expected to increase evaporation which will likely result in a general lowering of water levels in the Great Lakes (up to 1 m). This will lead to warmer water temperatures, and will affect the timing of seasonal mixing and overall water quality.

Climate Variable:

Climate Variable	General/Specific Changes Expected	Seasonal/Geographic Pattern of Change	Supported by Science/Source

Temperature	Southern Ontario is expected to experience temperature increases of 2 to 6C	Under HadCM3, annual mean warming for Toronto (2050s) is expected to increase by 2.5 to 4.0C (NRCan, 2006); Under CGCM2 A2 annual temperature increases in southern Ontario will be more pronounced in the winter (3 to 6C) then in the summer (2 to 5C) (MNR, 2007b).	Natural Resources Canada (NRCan) 2006, Coastal Zones and Climate Change on the Great Lakes: Final Report; Ontario Ministry of Natural Resources (MNR) 2007, Climate Change Projections for Ontario: Practical Information for Policymakers and Planners.
Temperature	Southern Ontario is expected to experience a decline in cold extremes	Winter cold extremes that now occur on average once every 10 years will likely occur less than once every 80 years	Environment Canada (EC) 2004, Understanding Climate Change: The Science, Impacts and Actions to be Taken.

Precipitation	Annual precipitation is expected to become more variable and the ratio of snow to annual precipitation is expected to decrease	Under HadCM3 Toronto is projected to experience total annual precipitation increases of 2 to 13% (NRCan, 2006). Under CGCM2 A2, however, southern Ontario, south of Owen Sound to Pembroke, is expected to experience a decline in precipitation of up to 10%, while north of Owen Sound to Pembroke, precipitation is expected to increase by 10% (MNR, 2007b)	Natural Resources Canada (NRCan) 2006, Coastal Zones and Climate Change on the Great Lakes: Final Report; Ontario Ministry of Natural Resources (MNR) 2007, Climate Change Projections for Ontario: Practical Information for Policymakers and Planners.
		Overall increase in occurrence and intensity of extreme rainfall events, decline in the total number of winter storm events	Natural Resources Canada (NRCan) 2006, Coastal Zones and Climate Change on the Great Lakes: Final Report
		Southern Ontario could experience a decrease in freezing rain events during the months of November, April and May (10% by 2050, and 15% by 2080). Future freezing rain events could increase during the months of December, January and February (40% by 2050, and 45% by 2080)	Cheng et al. 2007. Possible impacts of climate change on freezing rain in south-central Canada using downscaled future climate scenarios. Natural Hazards and Earth System Sciences

Smog	Southern Ontario is expected to experience an increase in occurrence of smog advisory days	In 2005 Ontario recorded 53 smog advisory days, exceeding the previous records of 27 smog advisory days in 2002, this trend is expected to continue	Ontario Ministry of the Environment (MOE) 2007, http://www.ene.gov.on.ca/en/air/ climatechange/index.php

Emissions/GHGs	Atmospheric CO2 is expected to increase	Canadian Coupled Global Circulation Model (CGCM2) A2, a mid-range scenario, projects atmospheric CO2 concentration of 1320 ppm by 2100	Ontario Ministry of Natural Resources (MNR) 2007, Climate Change Projections for Ontario: Practical Information for Policymakers and Planners.
Emissions/GHGs		Data collected from polar ice cores show that concentrations of CO2 have increased by 30% since the start of the industrial revolution and are expected to reach 970 ppm by 2100	Environment Canada (EC) 2004, Understanding Climate Change: The Science, Impacts and Actions to be Taken.

References

Cheng, C.S., H. Auld, G. Li, J. Klaassen, and Q. Li. 2007. Possible impacts of climate change on freezing rain in south-central Canada using downscaled future climate scenarios. Natural Hazards and Earth System Sciences 7, 71-87.

EC (Environment Canada). 2004. Understanding Climate Change: The Science, Impacts and Actions to be Taken. Presented to the Toronto and Region Conservation Authority by Joan Klaassen.

IPCC (International Panel on Climate Change) 2007. Climate Change 2007: The Physical Science Basis, Summary for Policy Makers. International Panel on Climate Change. http://ipcc-wg1.ucar.edu/wg1/

MNR (Ontario Ministry of Natural Resources). 2007. Climate Change Projections for Ontario: Practical Information for Policymakers and Planners. Ontario Ministry of Natural Resources.

MOE (Ministry of the Environment, Ontario) 2007. http://www.ene.gov.on.ca/en/air/climatechange/index.php

NRCan (Natural Resources Canada) 2004. Climate Change Impacts and Adaptation: A Canadian Perspective. Natural Resources Canada. http://adaptation.nrcan.gc.ca/perspective_e.asp

NRCan (Natural Resources Canada) 2006. Coastal Zones and Climate Change on the Great Lakes: Final Report. Natural Resources Canada, Climate Change Action Fund. http://adaptation.nrcan.gc.ca/projdb/pdf/coastal1_e.pdf

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Impact and System Response:

Sector	Impact and System Response

Terrestrial Ecosystems (including urban forests)	Northward expansion of the Carolinian Zone. Most tree species migrate at a rate of only 4 to 200 km/century. Models predict a northward shift of more than 500 km /century. Unable to keep pace with climate change, woodlots are more likely to become stressed or die out, leading to loss of native biodiversity. (EC, 2005) While warmer landscapes will support greater biodiversity, the increase in future species may originate from invasion of exotics and loss of native biodiversity. Species loss as a result of habitat change (e.g. grassland birds will shift northwards but their habitat will not likely move at the same rate). Species loss as a result of inability to compete with invasive species and decoupled species relationships. Proliferation of over-wintering insect pests which will impact agricultural and forestry production. Where land use creates barriers to dispersal of native species and facilitates dispersal of exotic species, climate change in urban areas/ human dominated landscapes of GTA is likely to produce more exotic species than native species. Plants growing earlier in the spring with earlier germination leaf out and flowering times Increased decline of some tree species such as pines and maples. Changes in carbon storage function (potential shift from sinks to sources). Uncertain impacts on wetlands: structure, function, hydrology

Water Quantity and Quality (Hydrology)	Annual volumes of precipitation in TRCA's jurisdiction may increase or decrease; patterns and distribution are expected to change. As a result of increased average temperatures, the ratio of snow to total annual precipitation will likely decrease. There is potential for a shorter snow accumulation period, greater winter runoff and reduced summer flows. There may be an increase in the frequency and magnitude of storm events, increased surface runoff, as well as erosion and sediment loading in rivers. The volume of water available to both surface and groundwater systems could potentially increase or decrease depending on the relative proportion of temperature and precipitation changes, the seasonal distribution of change, and the change in the frequency of intense (storm)precipitation events. These changes may result in potential impacts on the groundwater systems. Change in the pattern of water supply which will increase pressure on source water resources and impact municipal management.

Aquatic Ecosystems (including Coastal Eco-systems)	As surface temperatures increase, water temperatures are expected to rise as well. Warmer waters may result in sensitive aquatic species moving upstream to maintain temperature conditions resulting in the loss of cold water fisheries, e.g. trout and salmon; the invasion of non-native species such as common carp and zebra mussels which will alter fish community Reduced ice cover, which when coupled with an increase in extreme events, will increase erosion and sediment loading. Rapid spring warming may cause shallower and steeper thermoclines

Infrastructure	Increased risk to municipal infrastructure, (e.g. increase in road washouts, increased stress on flood water management system, increased capacity demands on storm sewers and stormwater management systems) i Increased cost of insurance as a result of flooded basements and buildings and extreme weather (insurance losses multiplied more than 13 times from 1960 to 1999 (CAP, 2007). Increase in temperature and extreme events may pose a risk to the integrity and longevity of built heritage structures. Increase in freeze/thaw cycles may create premature deterioration of roads.

Energy	Peak summer power demands has already shifted the way energy is produced and distributed. Overall energy demand in the GTA is increasing on a annual basis and with growth targets of 2.9 %, it will grow further. Approximately 80% of the province's electricity supply will need to be replaced with a combination of new supply/peak demand management and conservation.

Human Communities (Human Health/Recreation)	Warmer temperatures exacerbate air quality problems in urban centres and may result in increased production of ozone and other photochemical components of smog; increased occurrence of human respirator difficulties; risk of solar radiation during outdoor recreation pursuits; and likely increase in vector-borne diseases such as malaria, lyme and West Nile virus; water borne diseases and heat- related illnesses. Extreme weather events may further cause risks to human life and property due to flooding. Changes in flora and fauna may have impacts on nature based recreation such as bird watching, angling and nature viewing; however, climate change may result in a net positive impact on nature-based tourism and outdoor recreation in our jurisdiction due to increasing season length for warm weather activities. Canoeing may be limited due to potential reduction in baseflow in some lower tributaries of the watersheds. Loss of swimming days due to beach closures because of bacteria.

Agriculture	Both positive and negative impacts are expected -longer frost free periods could extend the growing season and potential for new crop varieties. Potential for more local production in the GTA. High plant productivity due to increased CO2. Climate variability - severe drought, floods or pests could damage crops. High temperature may cause lower dairy production.

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